libstdc++
streambuf
1 // Stream buffer classes -*- C++ -*-
2 
3 // Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
4 // 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
5 //
6 // This file is part of the GNU ISO C++ Library. This library is free
7 // software; you can redistribute it and/or modify it under the
8 // terms of the GNU General Public License as published by the
9 // Free Software Foundation; either version 3, or (at your option)
10 // any later version.
11 
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
16 
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
20 
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
25 
26 /** @file streambuf
27  * This is a Standard C++ Library header.
28  */
29 
30 //
31 // ISO C++ 14882: 27.5 Stream buffers
32 //
33 
34 #ifndef _GLIBXX_STREAMBUF
35 #define _GLIBXX_STREAMBUF 1
36 
37 #pragma GCC system_header
38 
39 #include <bits/c++config.h>
40 #include <iosfwd>
41 #include <bits/localefwd.h>
42 #include <bits/ios_base.h>
43 #include <bits/cpp_type_traits.h>
44 #include <ext/type_traits.h>
45 
46 _GLIBCXX_BEGIN_NAMESPACE(std)
47 
48  template<typename _CharT, typename _Traits>
49  streamsize
50  __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
51  basic_streambuf<_CharT, _Traits>*, bool&);
52 
53  /**
54  * @brief The actual work of input and output (interface).
55  *
56  * This is a base class. Derived stream buffers each control a
57  * pair of character sequences: one for input, and one for output.
58  *
59  * Section [27.5.1] of the standard describes the requirements and
60  * behavior of stream buffer classes. That section (three paragraphs)
61  * is reproduced here, for simplicity and accuracy.
62  *
63  * -# Stream buffers can impose various constraints on the sequences
64  * they control. Some constraints are:
65  * - The controlled input sequence can be not readable.
66  * - The controlled output sequence can be not writable.
67  * - The controlled sequences can be associated with the contents of
68  * other representations for character sequences, such as external
69  * files.
70  * - The controlled sequences can support operations @e directly to or
71  * from associated sequences.
72  * - The controlled sequences can impose limitations on how the
73  * program can read characters from a sequence, write characters to
74  * a sequence, put characters back into an input sequence, or alter
75  * the stream position.
76  * .
77  * -# Each sequence is characterized by three pointers which, if non-null,
78  * all point into the same @c charT array object. The array object
79  * represents, at any moment, a (sub)sequence of characters from the
80  * sequence. Operations performed on a sequence alter the values
81  * stored in these pointers, perform reads and writes directly to or
82  * from associated sequences, and alter "the stream position" and
83  * conversion state as needed to maintain this subsequence relationship.
84  * The three pointers are:
85  * - the <em>beginning pointer</em>, or lowest element address in the
86  * array (called @e xbeg here);
87  * - the <em>next pointer</em>, or next element address that is a
88  * current candidate for reading or writing (called @e xnext here);
89  * - the <em>end pointer</em>, or first element address beyond the
90  * end of the array (called @e xend here).
91  * .
92  * -# The following semantic constraints shall always apply for any set
93  * of three pointers for a sequence, using the pointer names given
94  * immediately above:
95  * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
96  * also be non-null pointers into the same @c charT array, as
97  * described above; otherwise, @e xbeg and @e xend shall also be null.
98  * - If @e xnext is not a null pointer and @e xnext < @e xend for an
99  * output sequence, then a <em>write position</em> is available.
100  * In this case, @e *xnext shall be assignable as the next element
101  * to write (to put, or to store a character value, into the sequence).
102  * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
103  * input sequence, then a <em>putback position</em> is available.
104  * In this case, @e xnext[-1] shall have a defined value and is the
105  * next (preceding) element to store a character that is put back
106  * into the input sequence.
107  * - If @e xnext is not a null pointer and @e xnext< @e xend for an
108  * input sequence, then a <em>read position</em> is available.
109  * In this case, @e *xnext shall have a defined value and is the
110  * next element to read (to get, or to obtain a character value,
111  * from the sequence).
112  */
113  template<typename _CharT, typename _Traits>
114  class basic_streambuf
115  {
116  public:
117  //@{
118  /**
119  * These are standard types. They permit a standardized way of
120  * referring to names of (or names dependant on) the template
121  * parameters, which are specific to the implementation.
122  */
123  typedef _CharT char_type;
124  typedef _Traits traits_type;
125  typedef typename traits_type::int_type int_type;
126  typedef typename traits_type::pos_type pos_type;
127  typedef typename traits_type::off_type off_type;
128  //@}
129 
130  //@{
131  /// This is a non-standard type.
132  typedef basic_streambuf<char_type, traits_type> __streambuf_type;
133  //@}
134 
135  friend class basic_ios<char_type, traits_type>;
136  friend class basic_istream<char_type, traits_type>;
137  friend class basic_ostream<char_type, traits_type>;
138  friend class istreambuf_iterator<char_type, traits_type>;
139  friend class ostreambuf_iterator<char_type, traits_type>;
140 
141  friend streamsize
142  __copy_streambufs_eof<>(__streambuf_type*, __streambuf_type*, bool&);
143 
144  template<bool _IsMove, typename _CharT2>
145  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
146  _CharT2*>::__type
147  __copy_move_a2(istreambuf_iterator<_CharT2>,
148  istreambuf_iterator<_CharT2>, _CharT2*);
149 
150  template<typename _CharT2>
151  friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
152  istreambuf_iterator<_CharT2> >::__type
153  find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
154  const _CharT2&);
155 
156  template<typename _CharT2, typename _Traits2>
157  friend basic_istream<_CharT2, _Traits2>&
158  operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
159 
160  template<typename _CharT2, typename _Traits2, typename _Alloc>
161  friend basic_istream<_CharT2, _Traits2>&
162  operator>>(basic_istream<_CharT2, _Traits2>&,
163  basic_string<_CharT2, _Traits2, _Alloc>&);
164 
165  template<typename _CharT2, typename _Traits2, typename _Alloc>
166  friend basic_istream<_CharT2, _Traits2>&
167  getline(basic_istream<_CharT2, _Traits2>&,
168  basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
169 
170  protected:
171  //@{
172  /**
173  * This is based on _IO_FILE, just reordered to be more consistent,
174  * and is intended to be the most minimal abstraction for an
175  * internal buffer.
176  * - get == input == read
177  * - put == output == write
178  */
179  char_type* _M_in_beg; // Start of get area.
180  char_type* _M_in_cur; // Current read area.
181  char_type* _M_in_end; // End of get area.
182  char_type* _M_out_beg; // Start of put area.
183  char_type* _M_out_cur; // Current put area.
184  char_type* _M_out_end; // End of put area.
185 
186  /// Current locale setting.
187  locale _M_buf_locale;
188 
189  public:
190  /// Destructor deallocates no buffer space.
191  virtual
192  ~basic_streambuf()
193  { }
194 
195  // [27.5.2.2.1] locales
196  /**
197  * @brief Entry point for imbue().
198  * @param loc The new locale.
199  * @return The previous locale.
200  *
201  * Calls the derived imbue(loc).
202  */
203  locale
204  pubimbue(const locale &__loc)
205  {
206  locale __tmp(this->getloc());
207  this->imbue(__loc);
208  _M_buf_locale = __loc;
209  return __tmp;
210  }
211 
212  /**
213  * @brief Locale access.
214  * @return The current locale in effect.
215  *
216  * If pubimbue(loc) has been called, then the most recent @c loc
217  * is returned. Otherwise the global locale in effect at the time
218  * of construction is returned.
219  */
220  locale
221  getloc() const
222  { return _M_buf_locale; }
223 
224  // [27.5.2.2.2] buffer management and positioning
225  //@{
226  /**
227  * @brief Entry points for derived buffer functions.
228  *
229  * The public versions of @c pubfoo dispatch to the protected
230  * derived @c foo member functions, passing the arguments (if any)
231  * and returning the result unchanged.
232  */
233  __streambuf_type*
234  pubsetbuf(char_type* __s, streamsize __n)
235  { return this->setbuf(__s, __n); }
236 
237  pos_type
238  pubseekoff(off_type __off, ios_base::seekdir __way,
239  ios_base::openmode __mode = ios_base::in | ios_base::out)
240  { return this->seekoff(__off, __way, __mode); }
241 
242  pos_type
243  pubseekpos(pos_type __sp,
244  ios_base::openmode __mode = ios_base::in | ios_base::out)
245  { return this->seekpos(__sp, __mode); }
246 
247  int
248  pubsync() { return this->sync(); }
249  //@}
250 
251  // [27.5.2.2.3] get area
252  /**
253  * @brief Looking ahead into the stream.
254  * @return The number of characters available.
255  *
256  * If a read position is available, returns the number of characters
257  * available for reading before the buffer must be refilled.
258  * Otherwise returns the derived @c showmanyc().
259  */
260  streamsize
261  in_avail()
262  {
263  const streamsize __ret = this->egptr() - this->gptr();
264  return __ret ? __ret : this->showmanyc();
265  }
266 
267  /**
268  * @brief Getting the next character.
269  * @return The next character, or eof.
270  *
271  * Calls @c sbumpc(), and if that function returns
272  * @c traits::eof(), so does this function. Otherwise, @c sgetc().
273  */
274  int_type
275  snextc()
276  {
277  int_type __ret = traits_type::eof();
278  if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(),
279  __ret), true))
280  __ret = this->sgetc();
281  return __ret;
282  }
283 
284  /**
285  * @brief Getting the next character.
286  * @return The next character, or eof.
287  *
288  * If the input read position is available, returns that character
289  * and increments the read pointer, otherwise calls and returns
290  * @c uflow().
291  */
292  int_type
293  sbumpc()
294  {
295  int_type __ret;
296  if (__builtin_expect(this->gptr() < this->egptr(), true))
297  {
298  __ret = traits_type::to_int_type(*this->gptr());
299  this->gbump(1);
300  }
301  else
302  __ret = this->uflow();
303  return __ret;
304  }
305 
306  /**
307  * @brief Getting the next character.
308  * @return The next character, or eof.
309  *
310  * If the input read position is available, returns that character,
311  * otherwise calls and returns @c underflow(). Does not move the
312  * read position after fetching the character.
313  */
314  int_type
315  sgetc()
316  {
317  int_type __ret;
318  if (__builtin_expect(this->gptr() < this->egptr(), true))
319  __ret = traits_type::to_int_type(*this->gptr());
320  else
321  __ret = this->underflow();
322  return __ret;
323  }
324 
325  /**
326  * @brief Entry point for xsgetn.
327  * @param s A buffer area.
328  * @param n A count.
329  *
330  * Returns xsgetn(s,n). The effect is to fill @a s[0] through
331  * @a s[n-1] with characters from the input sequence, if possible.
332  */
333  streamsize
334  sgetn(char_type* __s, streamsize __n)
335  { return this->xsgetn(__s, __n); }
336 
337  // [27.5.2.2.4] putback
338  /**
339  * @brief Pushing characters back into the input stream.
340  * @param c The character to push back.
341  * @return The previous character, if possible.
342  *
343  * Similar to sungetc(), but @a c is pushed onto the stream instead
344  * of "the previous character". If successful, the next character
345  * fetched from the input stream will be @a c.
346  */
347  int_type
348  sputbackc(char_type __c)
349  {
350  int_type __ret;
351  const bool __testpos = this->eback() < this->gptr();
352  if (__builtin_expect(!__testpos ||
353  !traits_type::eq(__c, this->gptr()[-1]), false))
354  __ret = this->pbackfail(traits_type::to_int_type(__c));
355  else
356  {
357  this->gbump(-1);
358  __ret = traits_type::to_int_type(*this->gptr());
359  }
360  return __ret;
361  }
362 
363  /**
364  * @brief Moving backwards in the input stream.
365  * @return The previous character, if possible.
366  *
367  * If a putback position is available, this function decrements the
368  * input pointer and returns that character. Otherwise, calls and
369  * returns pbackfail(). The effect is to "unget" the last character
370  * "gotten".
371  */
372  int_type
373  sungetc()
374  {
375  int_type __ret;
376  if (__builtin_expect(this->eback() < this->gptr(), true))
377  {
378  this->gbump(-1);
379  __ret = traits_type::to_int_type(*this->gptr());
380  }
381  else
382  __ret = this->pbackfail();
383  return __ret;
384  }
385 
386  // [27.5.2.2.5] put area
387  /**
388  * @brief Entry point for all single-character output functions.
389  * @param c A character to output.
390  * @return @a c, if possible.
391  *
392  * One of two public output functions.
393  *
394  * If a write position is available for the output sequence (i.e.,
395  * the buffer is not full), stores @a c in that position, increments
396  * the position, and returns @c traits::to_int_type(c). If a write
397  * position is not available, returns @c overflow(c).
398  */
399  int_type
400  sputc(char_type __c)
401  {
402  int_type __ret;
403  if (__builtin_expect(this->pptr() < this->epptr(), true))
404  {
405  *this->pptr() = __c;
406  this->pbump(1);
407  __ret = traits_type::to_int_type(__c);
408  }
409  else
410  __ret = this->overflow(traits_type::to_int_type(__c));
411  return __ret;
412  }
413 
414  /**
415  * @brief Entry point for all single-character output functions.
416  * @param s A buffer read area.
417  * @param n A count.
418  *
419  * One of two public output functions.
420  *
421  *
422  * Returns xsputn(s,n). The effect is to write @a s[0] through
423  * @a s[n-1] to the output sequence, if possible.
424  */
425  streamsize
426  sputn(const char_type* __s, streamsize __n)
427  { return this->xsputn(__s, __n); }
428 
429  protected:
430  /**
431  * @brief Base constructor.
432  *
433  * Only called from derived constructors, and sets up all the
434  * buffer data to zero, including the pointers described in the
435  * basic_streambuf class description. Note that, as a result,
436  * - the class starts with no read nor write positions available,
437  * - this is not an error
438  */
439  basic_streambuf()
440  : _M_in_beg(0), _M_in_cur(0), _M_in_end(0),
441  _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
442  _M_buf_locale(locale())
443  { }
444 
445  // [27.5.2.3.1] get area access
446  //@{
447  /**
448  * @brief Access to the get area.
449  *
450  * These functions are only available to other protected functions,
451  * including derived classes.
452  *
453  * - eback() returns the beginning pointer for the input sequence
454  * - gptr() returns the next pointer for the input sequence
455  * - egptr() returns the end pointer for the input sequence
456  */
457  char_type*
458  eback() const { return _M_in_beg; }
459 
460  char_type*
461  gptr() const { return _M_in_cur; }
462 
463  char_type*
464  egptr() const { return _M_in_end; }
465  //@}
466 
467  /**
468  * @brief Moving the read position.
469  * @param n The delta by which to move.
470  *
471  * This just advances the read position without returning any data.
472  */
473  void
474  gbump(int __n) { _M_in_cur += __n; }
475 
476  /**
477  * @brief Setting the three read area pointers.
478  * @param gbeg A pointer.
479  * @param gnext A pointer.
480  * @param gend A pointer.
481  * @post @a gbeg == @c eback(), @a gnext == @c gptr(), and
482  * @a gend == @c egptr()
483  */
484  void
485  setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
486  {
487  _M_in_beg = __gbeg;
488  _M_in_cur = __gnext;
489  _M_in_end = __gend;
490  }
491 
492  // [27.5.2.3.2] put area access
493  //@{
494  /**
495  * @brief Access to the put area.
496  *
497  * These functions are only available to other protected functions,
498  * including derived classes.
499  *
500  * - pbase() returns the beginning pointer for the output sequence
501  * - pptr() returns the next pointer for the output sequence
502  * - epptr() returns the end pointer for the output sequence
503  */
504  char_type*
505  pbase() const { return _M_out_beg; }
506 
507  char_type*
508  pptr() const { return _M_out_cur; }
509 
510  char_type*
511  epptr() const { return _M_out_end; }
512  //@}
513 
514  /**
515  * @brief Moving the write position.
516  * @param n The delta by which to move.
517  *
518  * This just advances the write position without returning any data.
519  */
520  void
521  pbump(int __n) { _M_out_cur += __n; }
522 
523  /**
524  * @brief Setting the three write area pointers.
525  * @param pbeg A pointer.
526  * @param pend A pointer.
527  * @post @a pbeg == @c pbase(), @a pbeg == @c pptr(), and
528  * @a pend == @c epptr()
529  */
530  void
531  setp(char_type* __pbeg, char_type* __pend)
532  {
533  _M_out_beg = _M_out_cur = __pbeg;
534  _M_out_end = __pend;
535  }
536 
537  // [27.5.2.4] virtual functions
538  // [27.5.2.4.1] locales
539  /**
540  * @brief Changes translations.
541  * @param loc A new locale.
542  *
543  * Translations done during I/O which depend on the current locale
544  * are changed by this call. The standard adds, "Between invocations
545  * of this function a class derived from streambuf can safely cache
546  * results of calls to locale functions and to members of facets
547  * so obtained."
548  *
549  * @note Base class version does nothing.
550  */
551  virtual void
552  imbue(const locale&)
553  { }
554 
555  // [27.5.2.4.2] buffer management and positioning
556  /**
557  * @brief Manipulates the buffer.
558  *
559  * Each derived class provides its own appropriate behavior. See
560  * the next-to-last paragraph of
561  * http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25s02.html
562  * for more on this function.
563  *
564  * @note Base class version does nothing, returns @c this.
565  */
566  virtual basic_streambuf<char_type,_Traits>*
567  setbuf(char_type*, streamsize)
568  { return this; }
569 
570  /**
571  * @brief Alters the stream positions.
572  *
573  * Each derived class provides its own appropriate behavior.
574  * @note Base class version does nothing, returns a @c pos_type
575  * that represents an invalid stream position.
576  */
577  virtual pos_type
578  seekoff(off_type, ios_base::seekdir,
579  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
580  { return pos_type(off_type(-1)); }
581 
582  /**
583  * @brief Alters the stream positions.
584  *
585  * Each derived class provides its own appropriate behavior.
586  * @note Base class version does nothing, returns a @c pos_type
587  * that represents an invalid stream position.
588  */
589  virtual pos_type
590  seekpos(pos_type,
591  ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
592  { return pos_type(off_type(-1)); }
593 
594  /**
595  * @brief Synchronizes the buffer arrays with the controlled sequences.
596  * @return -1 on failure.
597  *
598  * Each derived class provides its own appropriate behavior,
599  * including the definition of "failure".
600  * @note Base class version does nothing, returns zero.
601  */
602  virtual int
603  sync() { return 0; }
604 
605  // [27.5.2.4.3] get area
606  /**
607  * @brief Investigating the data available.
608  * @return An estimate of the number of characters available in the
609  * input sequence, or -1.
610  *
611  * "If it returns a positive value, then successive calls to
612  * @c underflow() will not return @c traits::eof() until at least that
613  * number of characters have been supplied. If @c showmanyc()
614  * returns -1, then calls to @c underflow() or @c uflow() will fail."
615  * [27.5.2.4.3]/1
616  *
617  * @note Base class version does nothing, returns zero.
618  * @note The standard adds that "the intention is not only that the
619  * calls [to underflow or uflow] will not return @c eof() but
620  * that they will return "immediately".
621  * @note The standard adds that "the morphemes of @c showmanyc are
622  * "es-how-many-see", not "show-manic".
623  */
624  virtual streamsize
625  showmanyc() { return 0; }
626 
627  /**
628  * @brief Multiple character extraction.
629  * @param s A buffer area.
630  * @param n Maximum number of characters to assign.
631  * @return The number of characters assigned.
632  *
633  * Fills @a s[0] through @a s[n-1] with characters from the input
634  * sequence, as if by @c sbumpc(). Stops when either @a n characters
635  * have been copied, or when @c traits::eof() would be copied.
636  *
637  * It is expected that derived classes provide a more efficient
638  * implementation by overriding this definition.
639  */
640  virtual streamsize
641  xsgetn(char_type* __s, streamsize __n);
642 
643  /**
644  * @brief Fetches more data from the controlled sequence.
645  * @return The first character from the <em>pending sequence</em>.
646  *
647  * Informally, this function is called when the input buffer is
648  * exhausted (or does not exist, as buffering need not actually be
649  * done). If a buffer exists, it is "refilled". In either case, the
650  * next available character is returned, or @c traits::eof() to
651  * indicate a null pending sequence.
652  *
653  * For a formal definition of the pending sequence, see a good text
654  * such as Langer & Kreft, or [27.5.2.4.3]/7-14.
655  *
656  * A functioning input streambuf can be created by overriding only
657  * this function (no buffer area will be used). For an example, see
658  * http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25.html
659  *
660  * @note Base class version does nothing, returns eof().
661  */
662  virtual int_type
663  underflow()
664  { return traits_type::eof(); }
665 
666  /**
667  * @brief Fetches more data from the controlled sequence.
668  * @return The first character from the <em>pending sequence</em>.
669  *
670  * Informally, this function does the same thing as @c underflow(),
671  * and in fact is required to call that function. It also returns
672  * the new character, like @c underflow() does. However, this
673  * function also moves the read position forward by one.
674  */
675  virtual int_type
676  uflow()
677  {
678  int_type __ret = traits_type::eof();
679  const bool __testeof = traits_type::eq_int_type(this->underflow(),
680  __ret);
681  if (!__testeof)
682  {
683  __ret = traits_type::to_int_type(*this->gptr());
684  this->gbump(1);
685  }
686  return __ret;
687  }
688 
689  // [27.5.2.4.4] putback
690  /**
691  * @brief Tries to back up the input sequence.
692  * @param c The character to be inserted back into the sequence.
693  * @return eof() on failure, "some other value" on success
694  * @post The constraints of @c gptr(), @c eback(), and @c pptr()
695  * are the same as for @c underflow().
696  *
697  * @note Base class version does nothing, returns eof().
698  */
699  virtual int_type
700  pbackfail(int_type /* __c */ = traits_type::eof())
701  { return traits_type::eof(); }
702 
703  // Put area:
704  /**
705  * @brief Multiple character insertion.
706  * @param s A buffer area.
707  * @param n Maximum number of characters to write.
708  * @return The number of characters written.
709  *
710  * Writes @a s[0] through @a s[n-1] to the output sequence, as if
711  * by @c sputc(). Stops when either @a n characters have been
712  * copied, or when @c sputc() would return @c traits::eof().
713  *
714  * It is expected that derived classes provide a more efficient
715  * implementation by overriding this definition.
716  */
717  virtual streamsize
718  xsputn(const char_type* __s, streamsize __n);
719 
720  /**
721  * @brief Consumes data from the buffer; writes to the
722  * controlled sequence.
723  * @param c An additional character to consume.
724  * @return eof() to indicate failure, something else (usually
725  * @a c, or not_eof())
726  *
727  * Informally, this function is called when the output buffer is full
728  * (or does not exist, as buffering need not actually be done). If a
729  * buffer exists, it is "consumed", with "some effect" on the
730  * controlled sequence. (Typically, the buffer is written out to the
731  * sequence verbatim.) In either case, the character @a c is also
732  * written out, if @a c is not @c eof().
733  *
734  * For a formal definition of this function, see a good text
735  * such as Langer & Kreft, or [27.5.2.4.5]/3-7.
736  *
737  * A functioning output streambuf can be created by overriding only
738  * this function (no buffer area will be used).
739  *
740  * @note Base class version does nothing, returns eof().
741  */
742  virtual int_type
743  overflow(int_type /* __c */ = traits_type::eof())
744  { return traits_type::eof(); }
745 
746 #if _GLIBCXX_DEPRECATED
747  // Annex D.6
748  public:
749  /**
750  * @brief Tosses a character.
751  *
752  * Advances the read pointer, ignoring the character that would have
753  * been read.
754  *
755  * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
756  */
757  void
758  stossc()
759  {
760  if (this->gptr() < this->egptr())
761  this->gbump(1);
762  else
763  this->uflow();
764  }
765 #endif
766 
767  private:
768  // _GLIBCXX_RESOLVE_LIB_DEFECTS
769  // Side effect of DR 50.
770  basic_streambuf(const __streambuf_type& __sb)
771  : _M_in_beg(__sb._M_in_beg), _M_in_cur(__sb._M_in_cur),
772  _M_in_end(__sb._M_in_end), _M_out_beg(__sb._M_out_beg),
773  _M_out_cur(__sb._M_out_cur), _M_out_end(__sb._M_out_cur),
774  _M_buf_locale(__sb._M_buf_locale)
775  { }
776 
777  __streambuf_type&
778  operator=(const __streambuf_type&) { return *this; };
779  };
780 
781  // Explicit specialization declarations, defined in src/streambuf.cc.
782  template<>
783  streamsize
784  __copy_streambufs_eof(basic_streambuf<char>* __sbin,
785  basic_streambuf<char>* __sbout, bool& __ineof);
786 #ifdef _GLIBCXX_USE_WCHAR_T
787  template<>
788  streamsize
789  __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
790  basic_streambuf<wchar_t>* __sbout, bool& __ineof);
791 #endif
792 
793 _GLIBCXX_END_NAMESPACE
794 
795 #ifndef _GLIBCXX_EXPORT_TEMPLATE
796 # include <bits/streambuf.tcc>
797 #endif
798 
799 #endif /* _GLIBCXX_STREAMBUF */